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Acrylic Varnish over an Oil Painting
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Posted
That’s a nasty error, it will certainly crack or flake off over time… how long that process will take I don’t know.
Robert is our resident expert on all things of this nature… I’m sure he’ll be able to give you a more definitive answer.
Hopefully, you’ve kept an inventory of your sales so that you can get them back and address the situation!
Posted
How old were the paintings before you varnished them? One of the problems with acrylic varnish is that it's almost impossible to remove, so I don't think you'd be able to just get it off and start again.
I'll look into this though - too late tonight, but will see what I can find out; a lot will depend on the actual varnish you used, and when you used it. Give us a clue about the brand, and any notes on the spray-can.
Posted
You might be in luck if you used a Winsor and Newton varnish - but if you didn't..... Well, let's find out what you did use, and then I can perhaps suggest what you can do; with some acrylic varnishes, removal is possible, but that will depend how dry the oil underneath is. You clearly already know that acrylic varnish is less than ideal, to put it gently ... a hard lesson learned. But - please name the brand.
Posted
You can remove acrylic varnish with isopropyl alcohol. It is very effective at removing dried acrylic paint too. It does not affect oil paint.
I tested this for you to be doubly sure of my facts. Here is a side by side of two paintings that were sitting by my wood burner waiting to die. The left one is acrylic 5 years old it took the paint off straight away, the right is oil about 3 years old unvarnished 
and unaffected.
and unaffected.
Posted
True, I'm sure (I've never tried it, though) but the success of that is still likely to depend on the composition of the varnish - there are many varieties of acrylic varnish - and, of course, the state of the oil paint, in this case, beneath it. Iso alcohol is good at removing many things - including paint which has not yet fully cured. Is it your experience Collette that long-dried acrylic paint can be removed in this way? ** I must have an abandoned acrylic somewhere that I could test it on..... you say the left panel is 5 years old, and the alcohol still removed the paint.... that's a bit worrying! Not entirely surprising, perhaps, but let us hope our acrylics don't get zealously cleaned with Iso at some point....
Anyway, fascinating stuff, more research to do....
** Redundant question, you've already answered that!
Posted
A bit more work and reading - to the original question: we are I think all agreed, and so is every source I've consulted, that acrylic varnish over oil is likely to peel, chip, or crack: how soon it will do this depends on a multitude of factors.
Some acrylic varnishes can be removed relatively easily (though I should find the process somewhat nerve-wracking). There are varnish removal products available - the Jacksons website offers at least one. These may be gentler than pure Iso alcohol - Collette found that the oil paint wasn't affected: my concern would be that paint that hadn't fully cured would be vulnerable: hard-dried paint should be OK,**
I don't see any reason to suppose that spray varnish would be any harder to remove than any other: and on balance, I'd recommend either going to a painting conservator and leaving the job with them while your fingers are crossed; or doing it yourself with the safest and best recommended product you can find. Certainly, that acrylic varnish needs to come off, if it will come off.
It remains my opinion that removing acrylic varnish over acrylic paint would be a very difficult job, particularly if the resin in the varnish is the same as the resin in the paint - I know of at least one brand I'd never subject to resin-based varnish removal. However yes - it should be possible to remove it over well-cured oil.
**Fingers crossed.